patch 9.1.0000: Vim 9.1 release

Problem:  Need a new release
Solution: Release Vim 9.1

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/usr_24.txt b/runtime/doc/usr_24.txt
index 361ce1b..72f43f0 100644
--- a/runtime/doc/usr_24.txt
+++ b/runtime/doc/usr_24.txt
@@ -1,4 +1,4 @@
-*usr_24.txt*	For Vim version 9.0.  Last change: 2018 Mar 18
+*usr_24.txt*	For Vim version 9.1.  Last change: 2018 Mar 18
 
 		     VIM USER MANUAL - by Bram Moolenaar